Hanoi and several provinces hoping to send Vietnamese workers to South Korea will not be allowed to join labor export programs unless they can reduce the number of migrants who run away or illegally overstay their visas once in the country, according to the labor ministry.

The ministry said more than 9,000 Vietnamese workers are currently working illegally in South Korea after their contracts had ended.

Nghe An Province in central Vietnam topped the list with 1,454 workers, followed by 948 from Hanoi. Other illegal workers came from Thanh Hoa and Ha Tinh Province neighboring Nghe An and the northern provinces of Hai Duong, Dam Dinh, Thai Binh, Bac Ninh, Hung Yen and Bac Giang.

The ministry has sent a statement to Hanoi and the provinces warning them that if they fail to reduce the number of illegal workers by the end of this month, it will consider putting a moratorium on recruiting any more workers from those areas.

Vietnam signed the first labor agreement with South Korea in 2004 and it expired at the end of last year. More than 80,000 Vietnamese workers have been sent to South Korea over the 10-year period and, according to ministry reports from September, around 63,000 Vietnamese migrants were still there at the time.

South Korea suspended labor cooperation in August 2012 after it found Vietnamese workers often did not leave the country after their labor contracts had ended. It resumed the agreement for one year in December 2013 after the rate of illegal workers dropped from 50 percent to 38 percent.

The country earlier this year signed a new agreement with Vietnam, allowing the latter to post 5,400 applications on the Internet so South Korean employers could select possible candidates from the list.

But labor officials are concerned that employment of additional Vietnamese migrants may be at risk as the rate of illegal workers is again on the rise.

The illegal workers, all coming from impoverished provinces, said they decided to overstay their visas because it was easier to find well-paying jobs in South Korea.

Vietnamese workers in South Korea receive a minimum wage of more than US$1,000 a month and work eight hours a day, five days a week. In Vietnamese factories, by comparison, they would receive a minimum wage of between VND2.15 and 3.1 million ($97-$140) and often have to work extra hours.

So far, Vietnam has fined 782 workers VND90 million each after they were caught staying in South Korea illegally. After the workers were arrested and deported, South Korea banned them from returning for up to 10 years.

Illegal workers coming home voluntarily by the end of this year will avoid the fine and only face a two-year ban, according to a government regulation put out in September.